AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Mobility Spectrometer Inverted Drift Tube Design for Classification of Submicrometric Sized Particles at Atmospheric Pressures
MD MINAL NAHIN, Carlos Larriba-Andaluz, IUPUI
Abstract Number: 337 Working Group: Instrumentation and Methods
Abstract In the Aerosol field, the Differential Mobility Analyzer (DMA) has been used almost exclusively for the classification of submicrometric sized particles. While the DMA has its strengths, its resolving power cannot compete with some of the newer Ion Mobility Spectrometers such as Drift Tubes(DTIMS) that are ubiquitously used in Analytical Chemistry. In this work, we propose a novel design of an Ion Mobility Spectrometer that couples the Drift Tube design with the flow field characteristics of the DMA:The Inverted Drift Tube (IDTIMS). In short, we propose the use of a small(9cmx5cm) tube where a linearly increasing electric field is used to oppose the migration of ions that are carried by a sheathed flow of inlet velocity Vgas. The ions are released at the entrance of the drift tube and will be fully stopped where there is an equilibrium between the flow velocity and drift velocity;Vgas=Vdrift=ZE. In order to push the ions into an electrometer or a Condensation Particle Counter, two methods have been devised: 1) Intermittent Push Flow where the field strength is subsequently reduced in “pushes” as the ions travel through the chamber and 2) Stopping Potential Separation where a fixed field is used to stop only one ion Mobility for as long as possible in order to achieve the maximum possible resolution.
Collision Statistical Models(SDS) have been used for the simulation of an IDTIMS using SIMION. Spherical Ions are allowed to migrate through the tube using a CFD generated flow field while 2D axisymmetric calculated electrical fields hinder their progress. Particles are allowed to diffuse and therefore a numerically predicted resolution can be achieved. In particular, spherical particles of up to 120nm in diameters can easily be resolved and the ITDIMS can differentiate two particles of 50nm and 49.5nm in diameter (Width at Half Maximum less than 1%).